1. Field of the Invention
The present invention relates to perpendicular magnetic recording media, and more particularly, to perpendicular magnetic recording media with a soft magnetic underlayer, a thickness and a structure of which are controlled to reduce noises.
2. Description of the Related Art
Recently, demands for recording media having larger areal recording density are rapidly being increased according to an increase of demands for magnetic disk devices. Conventionally, the magnetic recording media records data horizontally, however, a perpendicular magnetic recording method has been proposed to increase the areal recording density of the magnetic disk device. The perpendicular magnetic recording method magnetizes a magnetic recording layer, on which data is recorded, perpendicularly. The magnetic recording layer for such a perpendicular magnetization uses a magnetic material that can display relatively high magnetic anisotropy and coercivity.
FIG. 1 is a schematic cross-sectional view of a perpendicular magnetic recording device according to the related art. The perpendicular magnetic recording device includes a perpendicular magnetic recording medium and a magnetic head.
Referring to FIG. 1, the related perpendicular magnetic recording medium includes a soft magnetic underlayer 11, a recording layer 12, and a protective layer 13 that are sequentially formed on a substrate 10. An intermediate layer (not shown) may be further formed between the soft magnetic underlayer 11 and the recording layer 12. A magnetic head 15 is located above the perpendicular magnetic recording medium, and the magnetic head 15 includes a main pole and a return pole. The soft magnetic underlayer 11 is provided under the recording layer 12 in order to magnetize part A of the recording layer 12 efficiently and make writing of data easier.
The magnetic head applies a magnetic flux (M) to the recording layer 12 to magnetize the recording layer 12 and write the data. In more detail, when writing the data, the magnetic flux M discharged from the main pole magnetizes the recording layer 12 in a bit region unit, flows along the soft magnetic underlayer 11 under the recording layer 12, and then, returns to the return pole. Since a density of the magnetic flux discharged from the main pole is effectively transferred to the recording layer 12 without fluctuating, the recording layer 12 is more effectively magnetized by such a magnetic flux.
In the case of introducing such a soft magnetic underlayer 11, a saturation of the soft magnetic underlayer 11 should first be considered. To effectively prevent the saturation of the soft magnetic underlayer 11, the soft magnetic underlayer 11 should have a sufficient thickness and have a sufficient saturation magnetization of SUL (MS).
However, the thick soft magnetic underlayer 11 can result in serious magnetic domain noise. In addition, since the related soft magnetic underlayer 11 has a thickness of 100 nm or more, fabrication costs increase and a yield is degraded. In addition, in cases of recording data onto the recording layer 12 or reproducing the recorded data, noises may be generated on the soft magnetic underlayer 12 due to a stray field that is unintentionally generated by the magnetic head and a voice coil motor, and thereby, badly affecting the characteristics of the perpendicular magnetic recording media.